1. Field of the Invention
The present invention relates to an optical device with a quantum well, and more particularly, to an optical device with a quantum well with improved luminous efficiency and reliability.
2. Description of the Related Art
A quantum well is a structure formed by inserting between two different semiconductor layers a thin semiconductor layer having an energy bandgap much smaller than those of the two semiconductor layers. Carriers such as electrons or holes are confined in the quantum well by energy barriers. Studies on the quantum well have been actively conducted because an optical device with the quantum well can generate a large amount of light even at a small driving voltage.
FIGS. 1A and 1B are diagrams of a quantum well structure in a conventional optical device before and after applying a driving voltage, respectively.
Referring to FIG. 1A, an optical device comprises first and second barrier layers D and D′ having high conduction band energy and low valence band energy, and an active layer E formed between the first and second barrier layers D and D′ and having lower conduction band energy and higher valence band energy than the first and second barrier layers D and D′. Before applying a driving voltage, the conduction band energy of the active layer E corresponding to the bottom of the quantum well structure exhibits a constant energy level.
When driving voltage is applied, electrons and holes are rearranged so that the quantum well structure has an asymmetrical distribution of electrons and holes, as shown in FIG. 1B. Referring to FIG. 1B, the conduction band energy and the valence band energy of the active layer E change linearly with a slope. In this case, most electrons and holes are respectively distributed in the conduction band quantum well and the valence band quantum well in such a way to face each other diagonally, thereby decreasing the recombination efficiency of electrons and holes.
In particular, in an optical device in which an active layer having a quantum well structure is made of a GaInNAs semiconductor material, N. and In does not easily grow into a crystal due to unstable combination. Also, due to the addition of N, luminous efficiency and lifetime may be lowered.